Light-emitting conjugated oligomers comprising anthracene, naphthalene, and fluorene units have been synthesized to investigate three configurations of blue organic light-emitting diodes (OLEDs) that are designed to identify the origins of device instability. The transient OLED technique is employed to measure hole mobilities, which are found to be 3.1 x 10(-4), 8.9 x 10(-5), and 3.6 x 10(-5) cm(2) V-1 s(-1) for three different blue-light-emitting model compounds with varying fluorene content. A higher hole mobility through the emissive layer results in a wider recombination zone, which, in turn, is responsible for a longer device lifetime and a lower drive voltage at the expense of luminance yield.